Glucomannan scaffolding for three-dimensional tissue culture and engineering

ABSTRACT

The present invention provides a neutralized glucomannan scaffold capable of promoting cell growth and suitable for three-dimensional tissue culture and engineering. The present invention also provides methods for making and degrading the neutralized glucomannan scaffold. The present invention further provides a method of growing cells on a neutralized glucomannan scaffold.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/360,910, filed May 27, 2014, which is the National Stage ofInternational Application No. PCT/US2012/066982, which claims thebenefit of U.S. Provisional Application No. 61/564,553, filed Nov. 29,2011, which is incorporated in its entirety herein for all purposes.

BACKGROUND OF THE INVENTION

Engineering biomaterials to repair damaged or diseased tissues such ascardiac, bone, liver, corneal and skin is an active branch of researchin regenerative medicine. One approach being investigated is using cellscombined with biomaterial constructs, or scaffolds, that facilitate cellgrowth and differentiation to create functional tissues in vitro thatcan be implanted. Three-dimensional (3D) tissue culture systems, whichemulate key physical and molecular features of the extracellularmicroenvironment, provide tremendous advantages to tissue engineering.

Biomaterials may be naturally-derived, such as protein- andpolysaccharide-based biomaterials, or synthetic, for example, polymer-,peptide- and ceramic-based biomaterials. Rigorous exploration ofproperties such as immunogenicity, biodegradability, biocompatibility,ease of modification and permeability is required for the design anddevelopment of these biomaterials for clinical tissue engineering. Highporosity and adequate pore size, in particular, are important for cellseeding and diffusion of cells and nutrients.

The ready availability and biocompatibility of natural biomaterials suchhas collagen, alginate and chitosan have made these natural biomaterialsattractive substrates for 3D tissue culture. However, challenges withinconsistent mechanical properties and behavior of seeded cells limittheir clinical application.

For bone engineering, porosity and pore size of scaffolds have beenshown to be a critical factor. Prior studies have indicated that largerpores (˜200-300 μm) result in larger surface area that may promoteion/gas exchange, protein adsorption, and bone apatite mineralization(Karageorgiou et al. Biomaterials 2005 26:5474-91; Yuan et al.Biomaterials 1999 20:1799-806). It is also thought that a larger poresize may be necessary to vascularize implants and mimic the corticalsurface and cancellous interior of natural bone (Karageorgiou et al.Biomaterials 2005 26:5474-91). As such, there is a need for scaffoldswith large pores that can be seeded with bone cells and used for boneregeneration.

Glucomannan is a naturally-derived polysaccharide composed of a 1:1.6ratio of β-1,4 linked D-glucose to D-mannose with branches approximatelyevery 11 residues (Alonso-Sande et al. Eur J Pharm Biopharm. 200972:453-62). Glucomannan has a backbone of approximately 5-10%substituted acetyl groups that participate in hydrogen bonding andhydrophobic interactions that confers solubility. Hydrolysis of theacetyl group in the presence of alkali decreases the solubility ofglucomannan and results in aggregation followed by gel formation.Glucomannan is commonly used in foods as an emulsifier or thickener andis being investigated for biopharmaceutical applications due to itsgelling and biodegradable properties as well as its malleability to beshaped into films, beads and hydrogels. Glucomannan-based beads,microparticles, and nanoparticles have been developed for DNA and drugdelivery (Liu et al. Drug Deliv. 2007 14:397-402; Wang et al. Int JPharm. 2002 244:117-26; Wen et al. Int J Biol Macromol. 2008 42:256-63)with no significant signs of oral toxicity, skin sensitization,intestinal toxicity, embryotoxicity, or cell-aging observed (Konishi etal. Jpn J Exp Med. 1984 54:139-42).

Glucomannan has recently been investigated as composite scaffolds forchondrocyte culture and injectable scaffolds for cartilage regeneration(Kondo et al. J Tissue Eng Regen Med. 2009 3:361-7). This investigationresulted in the production of a konjac glucomannan/hyaluronic acidhydrogel, wherein cells are cultured and allowed to clump as asuspension in the gel. However, an exploration of developing glucomannanas a porous scaffold for tissue engineering applications has yet to beconducted.

Surprisingly, the present invention provides a glucomannan microporousmatrix capable of promoting cell growth and useful as a novelbiomaterial scaffold for 3D cell culture and tissue engineering as wellas in vivo tissue regeneration, for example, bone regeneration.

BRIEF SUMMARY OF THE INVENTION

It has been found that when a basic glucomannan scaffold is neutralized,the resulting neutralized glucomannan scaffold is useful as a matrix forthree-dimensional (3D) cell culture and tissue engineering. Theneutralized glucomannan scaffold has a pH that is suitable for efficientcell growth, and a porous structure that can permit diffusion of oxygen,nutrients, expressed products and cellular waste. Moreover, theneutralized glucomannan scaffold of the invention is amenable to surfacemodification to promote cell adhesion and proliferation. Thisnaturally-derived biomaterial scaffold is thermally stable, non-toxicand biodegradable and may mimic the natural three-dimensionalmicroenvironment of a wide range of cell types, such as osteoblasts,heptocytes, lymphocytes and stem cells.

In other embodiments, the present invention provides a method ofpreparing a neutralized glucomannan scaffold, including contacting abasic glucomannan scaffold having a pH of greater than about 8 with anaqueous solution at a pressure greater than or about atmosphericpressure, to form the neutralized glucomannan scaffold having a pH ofabout 7, thereby preparing the neutralized glucomannan scaffold.

In one embodiment, the present invention provides a method of preparinga neutralized glucomannan scaffold, including contacting a basicglucomannan scaffold having a pH of greater than about 8 with an aqueoussolution under vacuum pressure, to form the neutralized glucomannanscaffold having a pH of about 7, thereby preparing the neutralizedglucomannan scaffold.

In another embodiment, the present invention provides a method ofgrowing cells on a neutralized glucomannan scaffold, including heating areaction mixture of the neutralized glucomannan scaffold of the presentinvention and a cell, such that the cell multiplies, thereby growingcells on the neutralized glucomannan scaffold.

In another embodiment, the present invention provides a neutralizedglucomannan scaffold, prepared by contacting a basic glucomannanscaffold having a pH of greater than about 8, with an aqueous solutionto form the neutralized glucomannan scaffold having a pH of about 7.

In another embodiment, the present invention provides a neutralizedglucomannan scaffold, prepared by contacting a basic glucomannanscaffold having a pH of greater than about 8, with an aqueous solutionat a pressure greater than or about atmospheric pressure, to form theneutralized glucomannan scaffold having a pH of about 7, wherein thebasic glucomannan scaffold comprises a cell adhesion promoter.

In a further embodiment, the present invention provides a method ofdegrading the neutralized glucomannan scaffold of the present inventionby contacting the neutralized glucomannan scaffold with a degradingagent.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a scanning electron micrograph (surface topology) of thesurface of a glucomannan gel after sublimation of water. FIG. 1B shows ascanning electron micrograph (surface topology) of the surface of theinner structure of a glucomannan gel after sublimation of water. FIG. 1Cshows a scanning electron micrograph (surface topology) of humanmesenchymal stem cells (hMSC) seeded onto a glucomannan scaffold. FIG.1D shows a scanning electron micrograph (surface topology) of humanmesenchymal stem cells (hMSC) seeded onto a glucomannan scaffold.

FIG. 2 shows the effects of poly-L-lysine (PLL) on the adherence ofhMSC. PLL was added to the glucomannan mixture prior to gelling. hMSCshowed a significantly greater attachment to the resulting scaffoldcompared to control (p<0.05).

FIG. 3A shows bioluminescence images of hMSC cultured in the glucomannanscaffold. hMSC expressing firefly luciferase were seeded onto control orPLL-treated glucomannan scaffolds and imaged weekly. Cells cultured incontrol scaffolds showed an increase in the level of bioluminescenceover time. However, hMSC cultured in glucomannan scaffolds wererestricted to the site of seeding and showed no increase inbioluminescence. FIG. 3B shows bioluminescence photons per second dataof hMSC cultured in the glucomannan scaffold. hMSC expressing fireflyluciferase were seeded onto control or PLL-treated glucomannan scaffoldsand imaged weekly. Cells cultured in control scaffolds showed anincrease in the level of bioluminescence over time. However, hMSCcultured in glucomannan scaffolds were restricted to the site of seedingand showed no increase in bioluminescence.

FIG. 4A shows porous structures [200-300 μm] throughout a glucomannanscaffold prior to seeding (10× magnification). FIG. 4B shows an examplestructural morphology of hMSC seeded in the glucomannan scaffold (10×magnification). hMSC cultured in glucomannan scaffolds were stained withhematoxylin and eosin. FIG. 4C shows an example structural morphology ofhMSC seeded in the glucomannan scaffold (10× magnification). hMSCcultured in glucomannan scaffolds were stained with hematoxylin andeosin. FIG. 4D shows an example structural morphology of hMSC seeded inthe glucomannan scaffold (10× magnification). hMSC cultured inglucomannan scaffolds were stained with hematoxylin and eosin.

FIG. 5A shows expression of vimentin by hMSC cultured on culture plates.FIG. 5B shows expression of cytokeratin by hMSC cultured on cultureplates. FIG. 5C shows expression of vimentin by control cells seededonto a glucomannan scaffold. FIG. 5D shows expression of vimentin byhMSC cells seeded onto a glucomannan scaffold. FIG. 5E shows expressionof vimentin by flat cells lining irregularly shaped lumens. FIG. 5Fshows expression of vimentin by flat cells lining irregularly shapedlumens.

FIG. 6A shows cellular aggregates released from enzymatic digestion of aseeded glucomannan scaffold. FIG. 6B shows an outgrowth of cellsobserved on the cellular aggregates of FIG. 6A after washing andculturing overnight. FIG. 6C shows cellular release from enzymaticdigestion of a seeded glucomannan scaffold. Glucomannan scaffolds seededwith rhMSC were digested with 0.5, 5.0 and 50 units/ml of cellulase orβ-mannanase, and cells released from the scaffold were trypsinzed andcounted. Scaffolds incubated with cellulase showed an efficient releaseof cells at all concentrations. However, higher concentrations ofβ-mannanase resulted in suboptimal cell counts, whereas 0.5 unit/mlshowed results similar to cellulose.

FIG. 7 shows osteogenic differentiation of hMSC seeded onto glucomannanscaffolds. rhMSC seeded onto glucomannan scaffolds and cultured with andwithout osteogenic induction medium were stained with antibodies againsthuman osteopontin and bone sialoprotein II (BSP II). Induced hMSC showedboth osteopontin and BSP II expression. Uninduced cells initiated BSP IIexpression. Von Kossa staining showed mineral deposits in both uninducedand induced scaffolds. Magnification=10×.

FIG. 8A shows a scanning electron micrograph of CD34+ cell adherence tohMSC seeded onto glucomannan scaffolds and co-cultured with CD34+hematopoietic cells. FIG. 8B shows a scanning electron micrograph of theability of hMSC to “bridge” a pore in a glucomannan scaffold co-culturedwith hMSC and CD34+ hematopoietic cells. FIG. 8C shows a scanningelectron micrograph of CD34+ cell adherence to hMSC seeded ontoglucomannan scaffolds and co-cultured with CD34+ hematopoietic cells.FIG. 8B shows a scanning electron micrograph of CD34+ cell adherence tohMSC seeded onto glucomannan scaffolds and co-cultured with CD34+hematopoietic cells.

FIG. 9 shows a glucomannan scaffold before and after fabrication. Thisimage can be a part of Example 1. A glucomannan scaffold was fabricatedinto a shape of a vertebra (top right) and various shapes to fit intocell and culture vessels using either a knife or biopsy punch. Thisfigure provides a proof-of-concept example showing the scaffold of thisinvention can be fabricated into a variety of shapes resemblingdifferent organ systems.

FIG. 10 shows a gross image of a three-dimensional bone constructproduced using the neutralized glucomannan scaffold and human stemcells.

DETAILED DESCRIPTION OF THE INVENTION I. Definitions

As used herein, the term “glucomannan” refers to a naturally-derivedoligosaccharide composed of an approximately 1:1.6 ratio of β-1,4-linkedD-glucose to D-mannose with branches approximately every 11 residues(Alonso-Sande et al. Eur J Pharm Biopharm. 2009 72:453-462) andderivatives thereof. Glucomannan has a backbone of approximately 5-10%substituted acetyl groups that participate in hydrogen bonding andhydrophobic interactions that confer solubility. Exemplary glucomannanderivatives include, but are not limited to, water-soluble derivativessuch as O-alkyl derivatives and O-carboxyalkyl derivatives, derivativeswith various degrees of substitution (e.g., greater than or less than5-10% substituted acetyl groups), derivatives with various degrees ofoxidation, graft copolymers (e.g., acrylate and acrylamide copolymers)and salts thereof (e.g., quaternary ammonium salts thereof).

As used herein, the term “glucomannan gel” refers to a thermally stable,homogeneous suspension of crosslinked glucomannan. The glucomannan gelcan be formed in a variety of ways including, but not limited, byhydrolysis of the acetyl groups of glucomannan in the presence ofalkali. The glucomannan gel of the present invention can be modified topromote cell adhesion and proliferation. Exemplary modificationsinclude, but are not limited to, incorporation of a cell adhesionpromoter, chemical crosslinking, surface coating and introduction offunctional groups.

As used herein, the term “basic glucomannan scaffold” refers to athree-dimensional porous matrix formed by dehydrating a glucomannan geland having a pH of greater than about 8. The basic glucomannan scaffoldof the present invention may be modified to promote cell adhesion andproliferation. Exemplary modifications include, but are not limited to,incorporation of a cell adhesion promoter, surface coating, andintroduction of functional groups.

As used herein, the term “neutralized glucomannan scaffold” refers to aporous matrix that provides a three-dimensional environment suitable forcell culture and tissue engineering, including tissue regeneration, andhaving a pH of about 7. The neutralized glucomannan scaffold of thepresent invention is formed by neutralizing a basic glucomannan scaffoldwith an aqueous solution. The neutralized glucomannan scaffold of thepresent invention may be modified to promote cell adhesion andproliferation.

As used herein, the term “contacting” refers to the process of bringinginto contact at least two distinct species such that they can react. Itshould be appreciated, however, that the resulting reaction product canbe produced directly from a reaction between the added reagents or froman intermediate from one or more of the added reagents which can beproduced in the reaction mixture.

As used herein, the term “cell adhesion promoter” refers to a natural orsynthetic agent that enhances the adhesion or attachment of cells to aculture substrate, for example, by modifying the surface of thesubstrate, and/or by altering the surface charge. A cell adhesionpromoter may also enhance the adsorption of serum or extracellularmatrix proteins to the culture substrate. Exemplary cell adhesionpromoters include poly-L-lysine (PLL), poly-D-lysine (PDL), RGD peptide(RGD), KQAGDV, VAPG, FGL, amine groups, and extracellular matrixproteins such as fibronectin, elastin, collagen and laminin. The celladhesion promoter can also promote cell growth and cell differentiation.

As used herein, the term “buffered solution” refers to a homogeneousmixture of a buffer, or ionic compound that is a mixture of a weak acidand its conjugate base or a weak base and its conjugate acid and resistschanges in pH, in water. Exemplary buffers include, but are not limitedto, phosphate buffers, such as phosphate buffered saline (PBS), 3-{[tris(hydroxymethyl)methyl]amino}propanesulfonic acid (TAPS) 1,3-bis(tris(hydroxymethyl)methylamino)propane (BIS-TRIS),tris(hydroxymethyl)methylamine (TRIS),4-2-hydroxyethyl-1-piperazineethanesulfonic acid (HEPES), 2-{[tris(hydroxymethyl)methyl]amino}ethanesulfonic acid (TES),3-(N-morpholino)propanesulfonic acid (MOPS),piperazine-N,N′-bis(2-ethanesulfonic acid) (PIPES) and2-(N-morpholino)ethanesulfonic acid (MES).

As used herein, the term “acidic solution” refers to a homogeneousmixture of an acid, or substance that acts as a proton donor, in water.An acidic solution has a pH of less than 7. Exemplary acidic solutionsinclude, but are not limited to, hydrochloric acid, acetic acid,tartaric acid, malic acid and citric acid.

As used herein, the term “alkaline solution” refers to a basic solutioncontaining the salt of an alkali metal or alkaline earth metal, having apH greater than 7. Representative salts of alkali and alkali earthmetals include, but are not limited to, sodium hydroxide, sodiumcarbonate, potassium hydroxide, potassium carbonate, magnesiumhydroxide, magnesium carbonate, calcium hydroxide and calcium carbonate.

As used herein, the term “cell culture medium” refers to a substancethat supports the growth of cells. A cell culture medium typicallycontains a mixture of nutrients dissolved in a buffered solution, anddifferent types of cell culture media are useful for growing differenttypes of cells. Exemplary cell culture media include, but are notlimited to, Roswell Park Memorial Institute medium (RPMI), Dulbecco'sModified Eagle Medium (DMEM), Minimum Essential Medium (MEM), Dulbecco'sModified Eagle Medium: Nutrient Mixture F-12 medium (DMEM/F12), Iscove'sModified Dulbecco's Medium (IMDM), a National Collection of TypeCultures medium (NCTC) and Osteogenic Induction Medium (OIM).

As used herein, the term “degrading” refers to the breaking of thecrosslinking bonds that hold the scaffold together. The degrading isaccomplished using a degrading agent that hydrolyzes the glycosidiclinkages. The scaffold degrading agent can be any chemical or enzyme,such as endo-1,4 β-mannanase, mannan endo-1,4-β-mannosidase, glycosylhydrolase or cellulase, that does not digest cells attached to orembedded in a neutralized glucomannan scaffold. Other enzymes are usefulin the present invention.

II. Neutralized Glucomannan Scaffold

The present invention provides a neutralized glucomannan scaffold as anovel scaffold for three-dimensional cell culture and tissueengineering. The neutralized glucomannan scaffold provides a neutralenvironment and a highly porous structure and pore size suitable forculturing cells. The neutralized glucomannan scaffold can incorporate acell adhesion promoter. Moreover, the scaffold is homogenous, thermallystable, elastic, biocompatible and biodegradable, and can be made intoany shape and size suitable for 3D tissue culture and engineering by,for example, molding or cutting. The neutralized glucomannan scaffoldcan also be sterilized by autoclaving, making it useful for implantationand other in vivo applications.

Unlike alginate-based scaffolds (e.g., AlgiMatrix), the size of theneutralized glucomannan scaffold is not limited. In addition, theneutralized glucomannan scaffold can be modified for cell adherence in asingle step compared to the requirement for multiple, complex chemicalreactions for modifying alginate-based scaffolds.

The neutralized glucomannan scaffold can be prepared by any conditionssuitable to neutralize a basic glucomannan scaffold. Suitableconditions, for example, are those that can reduce the pH of theglucomannan scaffold from about 8 or greater, to about 7, in a suitableamount of time. For example, the basic glucomannan scaffold can beexposed to an aqueous solution in a heated environment, such as in anautoclave. Alternatively, suitable conditions involves continuousrinsing of the basic glucomannan scaffold using an aqueous solution fora suitable amount of time.

In some embodiments, the present invention provides a method forpreparing a neutralized glucomannan scaffold, including contacting abasic glucomannan scaffold having a pH of greater than about 8 with anaqueous solution at a pressure greater than or about atmosphericpressure, to form the neutralized glucomannan scaffold having a pH ofabout 7, thereby preparing the neutralized glucomannan scaffold.

The basic glucomannan scaffold can have any suitable pH equal to orgreater than about 8.0. Examples of suitable pH include about 8.0, 8.5,9.0, 9.5, 10.0, 10.5, 11.0 and higher.

The neutralized glucomannan scaffold can have any suitable pH of about7. Examples of suitable pH include from about 6.0 to about 8.0, such asfrom about 6.1 to about 7.9, from about 6.2 to about 7.8, from about 6.3to about 7.7, from about 6.4 to about 7.6, and from about 6.5 to about7.5.

The contacting can be performed at any suitable temperature. Forexample, the temperature can be room temperature, greater than roomtemperature or less than room temperature. In some embodiments, thetemperature is suitable to form steam. In some embodiments, thetemperature can be from about 0° C. to about 200° C., or from about 20°C. to about 200° C., or from about 20° C. to about 150° C., or fromabout 0° C. to about 130° C., or from about 20° C. to about 130° C., orfrom about 20° C. to about 100° C., or from about 20° C. to about 50°C., or from about 30° C. to about 50° C., or from about 50° C. to about200° C., or from about 75° C. to about 150° C., or from about 100° C. toabout 150° C. The temperature can also be about 0° C., 5, 10, 15, 20,25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150,160, 170, 180, 190 or about 200° C. The temperature can also be about30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44 or 45° C. Insome embodiments, the contacting can be performed at a temperature offrom about 0° C. to about 130° C. In other embodiments, the contactingcan be performed at a temperature of from about 20° C. to about 50° C.In still other embodiments, the contacting can be performed at atemperature of about 37° C. In some embodiments, the temperature isabout room temperature.

The contacting can be performed at any suitable pressure. In someembodiments, the contacting can be performed under reduced or increasedpressure. In some embodiments, the contacting is performed aboveatmospheric pressure. In some embodiments, the contacting can beperformed at a pressure of from about 0.1 psi to about 50 psi aboveatmospheric pressure. In some embodiments, the contacting can beperformed at a pressure of from about 1 psi to about 50 psi aboveatmospheric pressure. Other useful pressures include about 5, 10, 15,20, 25, 30, 35, 40, or about 45 psi above atmospheric pressure. Inanother embodiment, the contacting is performed at a pressure of fromabout 1 psi to about 30 psi above atmospheric pressure. In still otherembodiments, the contacting is performed at a pressure of from about 10psi to about 20 psi above atmospheric pressure. In some embodiments, thecontacting is performed at a pressure of about 15 psi above atmosphericpressure.

Any combination of temperature and pressure can be used to neutralizethe basic glucomannan scaffold. For example, the temperature can besufficient to generate steam, such as greater than 100° C., and thepressure can be greater than atmospheric pressure, such as from about0.1 psi to about 50 psi above atmospheric pressure. Other combinationsof temperature and pressure are useful in the present invention, such asat atmospheric temperature and pressure.

The contacting can be performed for any suitable period of time. In someembodiments, the period of time can be from about 1 minute to about 1month. In other embodiments, the contacting can be performed for fromabout 1 hour to about 1 week. In other embodiments, the contacting canbe performed for from about 1 hour to about 1 day. In still otherembodiments, the contacting can be performed for from about 8 to about20 hours.

The basic glucomannan scaffold can include a variety of othercomponents. For example, cell adhesion promoters, chemotactic moleculesand cell signaling molecules can be incorporated in the basicglucomannan scaffold.

In some embodiments, the basic glucomannan scaffold includes a suitablecell adhesion promoter. The cell adhesion promoters useful in thepresent invention are capable of adhering cells to the glucomannanscaffold. The cell adhesion promoters can also promote cell growthand/or promote cell differentiation. Exemplary cell adhesion promotersinclude, but are not limited to, poly-L-lysine (PLL), poly-D-lysine(PDL), RGD peptide (RGD), KQAGDV, VAPG, FGL, amine groups, andextracellular matrix proteins such as fibronectin, elastin, collagen andlaminin. In some embodiments, the cell adhesion promoter can bepoly-L-lysine (PLL), poly-D-lysine (PDL), RGD peptide (RGD), KQAGDV,VAPG, FGL, amine groups, fibronectin, elastin, collagen or laminin. Theextracellular matrix proteins can be from any suitable source,including, but not limited to, mammalian cells. In some embodiments, thecell adhesion promoter is PLL or RGD. In certain embodiments, the celladhesion promoter is PLL.

In some embodiments, the present invention provides a method forpreparing a neutralized glucomannan scaffold, including contacting abasic glucomannan scaffold having a pH of greater than about 8 with anaqueous solution to form the neutralized glucomannan scaffold having apH of about 7, wherein the basic glucomannan scaffold comprises a celladhesion promoter, thereby preparing the neutralized glucomannanscaffold.

In another embodiment, the basic glucomannan scaffold includes asuitable chemotactic molecule. Exemplary chemotactic molecules include,but are not limited to, serum, chemokines, morphogenetic proteins,growth factors, hyaluronan.

In another embodiment, the basic glucomannan scaffold includes asuitable cell signaling molecule. Exemplary cell signaling moleculesinclude, but are not limited to, extraceullar matrix proteins, peptidemotifs and growth factors.

The aqueous solution can have any suitable composition. The aqueoussolution can be water or a mixture of water and one or more non-alkalineagents that do not degrade or digest the neutralized glucomannanscaffold. Examples of suitable aqueous solution include, but are notlimited to, water, a buffered solution, an acidic solution and a cellculture medium.

In some embodiments, the aqueous solution is water, a buffered solution,an acidic solution or a cell culture medium.

In one embodiment, the aqueous solution is a buffered solution. Examplesof suitable buffered solutions include, but are not limited to, PBS,TAPS, BIS-TRIS propane, TRIS, HEPES, TES, MOPS, PIPES and MES. In someembodiments, the buffered solution is PBS, HEPES, MES, MOPS, TRIS orBIS-TRIS Propane. In certain embodiments, the buffered solution is PBS.

In another embodiment, the aqueous solution is an acidic solution.Examples of suitable acidic solutions include, but are not limited to,such as, but not limited to, hydrochloric acid, acetic acid, tartaricacid, malic acid and citric acid.

In another embodiment, the aqueous solution is a cell culture medium.Examples of suitable cell culture media include, but are not limited to,Roswell Park Memorial Institute medium (RPMI), Dulbecco's Modified EagleMedium (DMEM), Minimum Essential Medium (MEM), Dulbecco's Modified EagleMedium: Nutrient Mixture F-12 medium (DMEM/F12), Iscove's ModifiedDulbecco's Medium (IMDM), a National Collection of Type Cultures medium(NCTC) and Osteogenic Induction Medium (OIM). In some embodiments, thecell culture medium is Roswell Park Memorial Institute medium (RPMI),

Dulbecco's Modified Eagle Medium (DMEM), Minimum Essential Medium (MEM),Dulbecco's Modified Eagle Medium: Nutrient Mixture F-12 medium(DMEM/F12), Iscove's Modified Dulbecco's Medium (IMDM) or a NationalCollection of Type Cultures medium (NCTC).

The method of the invention can include a variety of additional steps.In some embodiments, the method further includes forming a reactionmixture including glucomannan powder, an alkaline solution and water;heating the reaction mixture at a temperature of from about 50° C. toabout 130° C. to form a glucomannan gel; increasing the pressure of theglucomannan gel to from about 0.1 psi to about 50 psi above atmosphericpressure; cooling the glucomannan gel to a temperature of less thanabout 50° C.; and removing the water from the glucomannan gel to formthe basic glucomannan scaffold. The basic glucomannan scaffold can befurther modified with a cell adhesion promoter described above.

The method of the invention can include a variety of additional steps.In some embodiments, the method further includes forming a reactionmixture including glucomannan powder, a cell adhesion promoter, analkaline solution and water; heating the reaction mixture at atemperature of from about 50° C. to about 130° C. to form a glucomannangel; increasing the pressure of the glucomannan gel to from about 0.1psi to about 50 psi above atmospheric pressure; cooling the glucomannangel to a temperature of less than about 50° C.; and removing the waterfrom the glucomannan gel to form the basic glucomannan scaffold.

The alkaline solution can be any solution containing the salt of analkali metal or alkaline earth metal. The alkaline solution is basic,having a pH greater than 7. Representative salts of alkali and alkaliearth metals include, but are not limited to, sodium hydroxide, sodiumcarbonate, potassium hydroxide, potassium carbonate, magnesiumhydroxide, magnesium carbonate, calcium hydroxide and calcium carbonate.In some embodiments, the alkaline solution comprises calcium hydroxide.

Glucomannan powder, the cell adhesion promoter and calcium hydroxide caneach be present in the reaction mixture in any suitable amount. In someembodiments, glucomannan powder is dissolved in water to provide aglucomannan solution containing from about 1% to about 5% w/vglucomannan in water.

In other embodiments, a cell adhesion promoter is added to theglucomannan solution as an aqueous solution containing from about0.0001% to about 20% w/v cell adhesion promoter. In one embodiment, acell adhesion promoter is added to the glucomannan solution as anaqueous solution containing from about 0.0001% to about 10% w/v celladhesion promoter. In another embodiment, a cell adhesion promoter isadded to the glucomannan solution as an aqueous solution containing fromabout 0.0001% to about 1% w/v cell adhesion promoter.

In still other embodiments, calcium hydroxide is added to theglucomannan solution in an amount to provide any suitable ratio ofcalcium hydroxide to glucomannan solution.

For example, the ratio of calcium hydroxide to glucomannan solution canbe from about 1:1000 to about 1:1 (w/w). In one embodiment, the ratio is1:10 (w/w). In another embodiment, calcium hydroxide is added to theglucomannan solution as an aqueous solution containing from about 1% toabout 2% w/v calcium hydroxide.

The reaction mixture can be formed at any suitable temperature, such asthose described above for the contacting step.

The reaction mixture can be heated to any suitable temperature. In someembodiments, the temperature can be greater than about 20, 25, 30, 35,40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120,125, 130° C. or higher. In some embodiments, the reaction mixture can beheated at a temperature of greater than about 130° C. In someembodiments, the reaction mixture can be heated to a temperature ofgreater than about 80° C.

The pressure of the glucomannan gel can be increased to any suitablepressure. In some embodiments, the pressure can be increased to fromabout 0.1 psi to about 200 psi above atmospheric pressure. In otherembodiments, the pressure is increased to from about 0.1 psi to about 50psi above atmospheric pressure. In certain embodiments, the pressure isincreased to about 30 psi.

The temperature of the glucomannan gel can be cooled to any suitabletemperature. In some embodiments, the temperature is cooled to aboutless than 80° C. In certain embodiments, the temperature is cooled toless than about 50° C.

The water can be removed from the glucomannan gel by any suitablemethod. In some embodiments, the removing step is performed byfreeze-drying, sublimation or thermally-induced phase separation work.In certain embodiments, the removing step is performed by sublimation.

The neutralized glucomannan scaffold can have any suitable pore size. Insome embodiments, the neutralized glucomannan scaffold has a pore sizeof from about 100 μm to about 400 μm. In other embodiments, theneutralized glucomannan scaffold can have a pore size of about 150 μm toabout 350 μm. In still other embodiments, the neutralized glucomannanscaffold can have a pore size of about 200 μm to about 300 μm.

In other embodiments, the present invention provides a method ofpreparing a neutralized glucomannan scaffold, including contacting abasic glucomannan scaffold having a pH of greater than about 8 with anaqueous solution at a pressure greater than or about atmosphericpressure, to form the neutralized glucomannan scaffold having a pH ofabout 7, thereby preparing the neutralized glucomannan scaffold.

The contacting can also be performed under any suitable vacuum pressure.In some embodiments, the contacting can be performed under a vacuumpressure of from about 0.1 mmHg to 760 mmHg. In some embodiments, thecontacting can be performed at a vacuum pressure of from about 10 mmHgto about 500 mmHg. Other useful vacuum pressures include about 20, 50,100, 200, 300, 400, or 500 mmHg. In another embodiment, the contactingis performed under a vacuum pressure of from about 10 psi to about 300mmHg. In still other embodiments, the contacting is performed at avacuum pressure of about 400 mmHg.

In another embodiment, the present invention provides a neutralizedglucomannan scaffold, prepared by contacting a basic glucomannanscaffold having a pH of greater than about 8, with an aqueous solutionto form the neutralized glucomannan scaffold having a pH of about 7.

In another embodiment, the present invention provides a neutralizedglucomannan scaffold, prepared by contacting a basic glucomannanscaffold having a pH of greater than about 8, with an aqueous solutionto form the neutralized glucomannan scaffold having a pH of about 7,wherein the basic glucomannan scaffold comprises a cell adhesionpromoter.

The present invention also provides a method of degrading theneutralized glucomannan scaffold of the present invention, by contactingthe neutralized glucomannan scaffold with a degrading agent. Thedegrading agent can be any suitable agent capable of hydrolyzing theglycosidic linkages. The degrading agent can be any chemical or enzyme.Enzymes useful as a degrading agent include, but are not limited to,endo-1,4 β-mannanase, mannan endo-1,4-β-mannosidase, glycosyl hydrolaseand cellulase. Other degrading agents include, but are not limited to,enzymes such as mannanase, pectinase, xylanase, glucanase, galactanase,or others.

The present invention also provides a composite scaffold comprising theneutralized glucomannan scaffold of the invention and a suitablebiomaterial. Suitable biomaterials include, protein- andpolysaccharide-based biomaterials and polymer-, peptide- andceramic-based biomaterials. Exemplary biomaterials include, but are notlimited to, extracellular matrix proteins (e.g., fibronectin elastin,collagen and laminin), alginate, chitosan, hyaluronic acid, Matrigel,gelatin, hydroxyapatite, calcium phosphates and bioactive glasses.

The methods of the present invention can be used to prepare a variety ofglucomannan scaffolds. In some embodiments, the present inventionprovides a neutral glucomannan scaffold. The neutral glucomannanscaffold can have a pH of about 7.

In some embodiments, the glucomannan scaffold can be a basic glucomannanscaffold having a pH equal to or greater than about 8.

In some embodiments, the glucomannan scaffold includes a cell adhesionpromoter. Any suitable cell adhesion promoter can be used in the presentinvention, such as those described above. In some embodiments, the celladhesion promoter can be poly-L-lysine (PLL), poly-D-lysine (PDL), RGDpeptide (RGD), KQAGDV, VAPG, FGL, amine groups, fibronectin, elastin,collagen or laminin. In some embodiments, the cell adhesion promoter canbe poly-L-lysine (PLL).

As described above, the glucomannan scaffold of the present inventioncan be prepared by a variety of methods, such as those described above.In some embodiments, the glucomannan scaffold of the present inventionis prepared by the methods of the present invention.

III. Growing Cells

The neutralized glucomannan scaffold of the present invention is usefulfor growing cells. Cells cultured on the neutralized glucomannanscaffold can interact with other cells and cell types and formaggregates. Cell adherence to and proliferation on the neutralizedglucomannan scaffold can be promoted by incorporation of a cell adhesionpromoter. Long-term culture is supported by the neutralized glucomannanscaffold. When cultured on the neutralized glucomannan scaffold, cellscan undergo proliferation and differentiation. For example, stem cellscan differentiate into functional lineages such as bone cells,cartilage, skin cells and blood cells. Accordingly, cellular processessuch as osteogenesis, chondrogenesis and hematopoiesis can be supportedon the neutralized glucomannan scaffold.

In another embodiment, the present invention provides a method ofgrowing cells on a neutralized glucomannan scaffold, including heating areaction mixture of the neutralized glucomannan scaffold of the presentinvention and a cell, such that the cell multiplies, thereby growingcells on the neutralized glucomannan scaffold. The cells can be grown invivo or in vitro.

Suitable cell types include, but are not limited to, somatic cells, suchas fibroblasts, skin cells, endothelial cells, epithelial cells,osteocytes, hepatocytes, neurons and chondrocytes, and stem andprogenitor cells, such as endothelial progenitor cells, embryonic stemcells, induced pluripotent stem cells, mesenchymal stem cells,hematopoietic stem cells, neuronal stem cells and muscle stem cells, andtheir derivatives. In some embodiments, the cell is a somatic cell. Inother embodiments, the cell is a stem cell or a progenitor cell. Incertain embodiments, the cell is a stem cell. In certain otherembodiments, the cell is a derivative of a stem cell.

The cells grown on the neutralized glucomannan scaffold can be recoveredby dissolving the glucomannan scaffold using any suitable agent. Forexample, the glucomannan scaffold can be dissolved using on or moreenzymes such as mannanase, cellulase, pectinase, xylanase, glucanase,galactanase, or others. Other agents for dissolving the glucomannanscaffold are known to those of skill in the art.

IV. Examples Example 1 Preparation of Glucomannan Scaffold

Glucomannan powder (1-5 g) was dissolved in 100 ml of distilled waterand stirred slowly for 5 min, then the solution was incubated at roomtemperature for 60 min. Calcium hydroxide solution (1.5%, 10 ml;Sigma-Aldrich, St. Louis, Mo., USA) was added to the glucomannansolutions and mixed vigorously for 1 min. Poly-L-lysine (Sigma-Aldrich)(0.001% to 1% w/v aqueous solution) was added to the mixture and heatedto 125° C. in a decloaking chamber for 30 min. After cooling to roomtemperature, glucomannan gels were soaked in distilled water overnight.Glucomannan gels were placed in culture dishes and then frozen in ablast freezer for 30 min at less than or equal to −50° C. Water wassublimated using a Vitris model 50-SRC-5 Sublimator. The shelftemperature was 12° C. with a condenser temperature of less than orequal to −58° C., and the vacuum was maintained at 80-100 millitorr. Theresulting glucomannan products were then packed in polyethylene bags,vacuum-sealed, and stored at less than or equal to −20° C. until use.

Neutralizing Glucomannan Scaffold

Water rinse prior to sublimation. Prior to sublimation of water, theglucomannan gel was washed several times in a large volume of water(approximately 5 liters) overnight (16-24 hours). After sublimation ofwater, the glucomannan scaffold was soaked in water, and the scaffoldwas pressed against a pH indicator. The scaffold showed a pH greaterthan 10. This indicated that washing of the glucomannan gel prior tosublimation of water and brief soaking of the glucomannan scaffold inwater after sublimation of water were insufficient for neutralizing thescaffold.

Conventional PBS wash. The glucomannan scaffold was washed in PBS onceor three times. This resulted in superficial (surface only)neutralization of the scaffold with an internal pH of greater than 9 or10. The glucomannan scaffold was also washed in PBS for 10, 30, and 60minutes. In all cases, these approaches resulted in superficialneutralization of the scaffold as described above. These findingsindicated that conventional washing of the scaffold in a bufferedsolution was insufficient for neutralization of the scaffold essentialfor culturing mammalian cells.

Heated PBS wash. The glucomannan scaffold was then incubated in PBS at95-100° C. for 30 minutes. A visible shrinkage of the scaffold wasnoted. After 30 minutes in boiling PBS, the scaffold was cut and pressedagainst a pH indicator. The outer region of the scaffold showed aneutral pH. However, the center of the scaffold showed condensation ofthe scaffold material, and this central region remained outside of theneutral range. In all cases described above, the scaffold stayed afloatindicating the presence of internal air pockets. Even after treatingwith boiling PBS for 30 minutes, the scaffold stayed afloat with anotable undesired change in the shape. These findings indicated that PBShad not completely displaced air trapped inside the scaffold, which ledto insufficient neutralization.

Pressurized PBS wash. The glucomannan scaffold was transferred to abeaker containing PBS and incubated at 120° C. in a pressurized chamberat 15 psi above atmospheric pressure for 30 minutes. No shrinkage of thescaffold was observed. The scaffold was submerged in PBS indicating acomplete displacement of air pockets with PBS. The glucomannan productswere cooled and stored in sterile PBS at 4° C. until use. A pH indicatorwas used to confirm that the pH of the scaffold was neutral. The entirescaffold showed a neutral pH without any change in the shape.

PBS wash under vacuum. The glucomannan scaffold was placed on a filter,and a vacuum pressure was applied to the bottom of the scaffold at 400mmHg. 1 ml of PBS was applied to the top of the scaffold 10 times. Afterthe procedure, a pH indicator was used to confirm that the pH of thescaffold was neutral. The entire scaffold showed a neutral pH withoutany change in the shape.

Example 2 Cell Growth on Neutralized Glucomannan Scaffold

Preparation of Cells. For human mesenchymal stem cells (hMSC), bonemarrow mononuclear cells (N=3, 1 female and 2 males, 20-40 yrs of age;Cambrex, East Rutherford, N.J., USA) were plated in 100 mm plates inα-MEM containing 20% fetal bovine serum (FBS), 1% L-glutamine, and 1%penicillin-streptomycin (Invitrogen, Carlsbad, Calif., USA) andincubated at 37° C. in 5% CO₂. Plates were washed withphosphate-buffered saline (PBS) three times every other day until cellsreached approximately 80% confluence. Cells were incubated with 0.25%trypsin-EDTA (Invitrogen) for 5 min at 37° C. Culture medium was addedto the cells in at a 1:1 ratio of trypsin-EDTA in order to inactivate.Cells were replated in culture medium at 5×10³ cells/cm². Cells werecultured up to 3 passages, cryopreserved using a controlled rateprotocol at every passage, and stored in liquid nitrogen until use. ForCD34+ cells, a subset of bone marrow mononuclear cells mentioned abovewere incubated with CD34 antibodies conjugated to PE (clone 581, BDBiosciences, San Jose, Calif., USA) in selection buffer (PBS containing0.5% bovine serum albumin-BSA and 2 mM EDTA in PBS) for 30 min at 4° C.Cells were washed in selection buffer and incubated with anti-PEmicrobeads (Miltenyi Biotec, Bergisch Gladbach, Germany) for 20 min at4° C. Cells were washed and resuspended in 500 μL of selection buffer,then applied to separation columns (Miltenyi Biotec). Separation columnswere washed three times, and retained cells were eluted with 1 ml ofselection buffer. A second round of separation was performed on theeluted cells.

Transduction. Cryopreserved hMSC from the second passage were thawed andtransduced with an HIV-1-derived lentiviral vector (1×10⁶ infectiousparticles/ml) expressing firefly luciferase under the control of the MNDpromoter in medium containing 4 mg/ml polybrene (Sigma-Aldrich). Cellswere incubated overnight, washed with PBS, and replenished with newmedium. Cells were cultured until they reached approximately 80%confluence. D-Luciferin was added to a subset of cells at 100 mg/ml, andbioluminescence was measured using a luminometer (Sirius, Berthold,Pforzheim, Germany) to confirm successful transduction.

Cell Seeding and Bioluminescence Imaging. Glucomannan scaffolds were cutapproximately 1 cm×1 cm×0.5 cm (width×depth×height), rehydrated, andwashed in PBS 5 times, and incubated in culture medium overnight. hMSC(1×10⁶/scaffold) were seeded onto glucomannan scaffolds in a 12-wellplate and cultured for 5 weeks. Cells were imaged using an IVIS 200imaging system (Caliper Life Sciences, Hopkinton, Mass., USA) every 3-4days for bioluminescence after adding 100 mg/ml of D-luciferin to eachwell, and images were analyzed using Living Image software (version 3.1,Caliper Life Sciences).

Scanning Electron Microscopy. Glucomannan scaffolds with and withoutseeded hMSC were dehydrated in a graded ethanol series. Scaffolds withhMSC were also co-cultured with CD34+ cells (1×10⁶) and incubated for 3days, followed by ethanol dehydration. Samples were mounted onto 12 mmaluminum pin stubs using carbon double sticky tabs, sputter-coated withgold using a PELCO Auto Sputter Coater SC-7, and viewed on the PhilipsXL30 TMP Scanning Electron Microscope.

Example 3 Enzyme Digestion

Lyophilized endo-1,4 β-mannanase (Megazyme) or cellulase obtained fromAspergillus niger (Sigma-Aldrich) were dissolved in culture medium.Scaffolds seeded with hMSC were incubated in 0.5 units/ml, 5.0 units/ml,or 50 units/ml of endo-1,4 β-mannanase or cellulase overnight.Degradation of scaffolds was checked visually. Cells were counted oncescaffolds were completely dissolved.

Example 4 Osteogenic Differentiation

Scaffolds seeded with hMSC were incubated in Osteogenic Induction Medium(Cambrex) or culture medium (control) with medium changed every 3-4 daysfollowing the manufacturer's recommendations. After 3 weeks, scaffoldswere fixed in 10% formalin followed by ethanol dehydration and embeddedin paraffin. Scaffolds were sectioned at 6 mm for immunohistochemistryand von Kossa staining.

Immunocytochemistry. Sections (5-6 μm) were treated with xylene followedby graded concentrations of ethanol. Slides were washed in PBS beforeheat-mediated antigen retrieval in citrate buffer (pH 6, Invitrogen) wasperformed. After cooling, decreasing concentrations of warm citratebuffer in PBS was applied followed by incubation with

Background Sniper (BioCare Medical, Concord, Calif., USA) which wasadded to each slide for 15 min. Slides were washed twice with PBSfollowed by incubation for 1 hr with blocking buffer (1% BSA, 0.1% fishskin gelatin, 0.1% Triton X, 0.05% tween-20) with 2% goat serum(Sigma-Aldrich). After two washes with PBS, primary antibody diluted inprimary antibody buffer (1% BSA, 0.1% fish skin gel) was incubated withslides overnight in a humidified chamber at 4° C. Primary antibodiesused were wide spectrum rabbit polyclonal anti-human cytokeratinantibody (Abcam, Cambridge, Mass., USA) diluted 1:50 and mousemonoclonal anti-human vimentin antibody (Sigma-Aldrich) diluted 1:100.For bone markers, rat monoclonal anti-human osteopontin antibody andmouse monoclonal anti-human bone sialoprotein II antibody (Millipore,Billerica, Mass., USA) were used at 1:200 dilutions. Mouse, rat, andrabbit IgG isotype controls (Invitrogen) were included. Slides werewashed with PBS for 5 min and incubated with secondary antibody for 1 hin the dark at room temperature. Secondary antibodies used were AlexaFluor 488 goat anti-mouse, Alexa Fluor 954 goat anti-rat, and AlexaFluor 594 goat anti-rabbit antibodies (Invitrogen) diluted 1:200 influorescence antibody diluent (BioCare Medical). After washing twicewith PBS, slides were mounted with ProLong Gold® antifade reagent withDAPI (Invitrogen) and a coverslip placed. Slides were observed under anOlympus BX61 microscope.

von Kossa Staining. Sections (5-6 μm) were treated with xylene followedby graded concentrations of ethanol. Sections were washed in distilledwater and incubated with 1% aqueous silver nitrate solution underultraviolet light for 1 h, then washed in distilled water and incubatedwith 5% sodium thiosulfate for 5 min. Sections were washed in distilledwater and incubated with 0.1% nuclear fast red solution for 5 minfollowed by dehydration through graded alcohol and xylene. A coverslipwas then placed on the slide in permanent mounting medium and observedunder an Olympus BX61 microscope.

Results are reported as the mean±standard error of the mean (SEM) andcalculated using Microsoft Excel (Microsoft, Redmond, Wash.).Statistical significance (p<0.05) was determined by two-sided Student'st-test analysis.

Although the foregoing invention has been described in some detail byway of illustration and example for purposes of clarity ofunderstanding, one of skill in the art will appreciate that certainchanges and modifications may be practiced within the scope of theappended claims. In addition, each reference provided herein isincorporated by reference in its entirety to the same extent as if eachreference was individually incorporated by reference.

What is claimed is:
 1. A method of preparing a neutralized glucomannanscaffold, the method comprising contacting a basic glucomannan scaffoldhaving a pH of greater than about 8 with an aqueous solution undervacuum pressure, wherein the aqueous solution is selected from the groupconsisting of a buffered solution, an acidic solution and a cell culturemedium, to form a neutralized glucomannan scaffold having a pH of about7, thereby preparing the neutralized glucomannan scaffold.
 2. The methodof claim 1, wherein the contacting is performed at a temperature of fromabout 0° C. to about 130° C.
 3. The method of claim 1, wherein thecontacting is performed at a temperature of from about 20° C. to about50° C.
 4. The method of claim 1, wherein the contacting is performed ata temperature of about 37° C.
 5. The method of claim 1, wherein thecontacting is performed at a pressure of from about 0.1 mmHg to about760 mmHg.
 6. The method of claim 1, wherein the contacting is performedfor a period of from about 1 minute to about 1 month.
 7. The method ofclaim 1, wherein the contacting is performed for a period of from about1 hour to about 1 week.
 8. The method of claim 1, wherein the contactingis performed for a period of from about 1 hour to about 1 day.
 9. Themethod of claim 1, wherein the contacting is performed for a period offrom about 8 to about 20 hours.
 10. The method of claim 1, wherein thebasic glucomannan scaffold further comprises a cell adhesion promoter.11. The method of claim 10, wherein the cell adhesion promoter isselected from the group consisting of poly-L-lysine (PLL), poly-D-lysine(PDL), RGD peptide (RGD), KQAGDV, VAPG, FGL, amine groups, fibronectin,elastin, collagen and laminin.
 12. The method of claim 11, wherein thecell adhesion promoter is poly-L-lysine (PLL).
 13. The method of claim10, wherein the method further comprises: forming a reaction mixturecomprising glucomannan powder, the cell adhesion promoter, an alkalinesolution and water; heating the reaction mixture at a temperature offrom about 50° C. to about 130° C. to form a glucomannan gel; increasingthe pressure of the glucomannan gel to from about 1 psi to about 200 psiabove atmospheric pressure; cooling the glucomannan gel to a temperatureof less than about 50° C.; and removing the water from the glucomannangel to form the basic glucomannan scaffold.
 14. The method of claim 13,wherein said pressure of the glucomannan gel is increased from about14.7 psi to about 50 psi above atmospheric pressure.
 15. The method ofclaim 13, wherein said removing step is performed by sublimation. 16.The method of claim 1, wherein the aqueous solution is a bufferedsolution.
 17. The method of claim 16, wherein the buffered solution isselected from the group consisting of PBS, HEPES, MES, MOPS, TRIS andBIS-TRIS Propane.
 18. The method of claim 16, wherein the bufferedsolution is PBS.
 19. The method of claim 1, wherein the aqueous solutionis a cell culture medium.
 20. The method of claim 19, wherein the cellculture medium is selected from the group consisting of a Roswell ParkMemorial Institute medium (RPMI), Dulbecco's Modified Eagle Medium(DMEM), Minimum Essential Medium (MEM), Dulbecco's Modified EagleMedium: Nutrient Mixture F-12 medium (DMEM/F12), Iscove's ModifiedDulbecco's Medium (IMDM), a National Collection of Type Cultures medium(NCTC) and Osteogenic Induction Medium (OIM).